1. Field of the Invention
This invention is directed to a TENS-type therapeutic device, in general, and to a microprocessor controlled TENS-type system, in particular.
2. Prior Art
U.S. Pat. No. 4,926,865 issued to Oman discloses a transcutaneous nerve stimulation device which is microcomputer controlled and includes input controls for controlling pulse parameters. The background discussion of this patent offers a good overview of the history of induced nerve stimulation and is therefore substantially reproduced below.
The use of electrical energy for the control of pain is well known. Although the specific physiological explanations underlying electrically derived pain control are not fully understood, the effects are quite real and provide a non-drug, non-surgical and non-psychiatric method of pain control which can be applied to a wide variety of painful conditions.
Transcutaneous electroneural stimulation (TENS) is a proven and accepted means of providing relief from many kinds of acute and chronic pain symptoms. It is an attractive alternative to pharmaceuticals since it has no addictive properties. In addition, there are no known side effects to properly applied TENS therapy.
Several theories have been developed to explain the neuro-physiological mechanisms through which TENS can affect pain perception. The earliest accepted explanation is the gate control theory, first postulated by Melzack and Wall in 1965 (Melzack, R. Wall P. D., "Pain mechanisms: a new theory," Science, Vol. 150, pp. 971-979, 1965). This theory used data from animal experiments to predict that stimulation of afferent nerves could inhibit transmission from both noxious and non-noxious inputs. However, subsequent research with commercially available stimulators has demonstrated that TENS efficacy cannot be explained by gate control theory alone (Schmidt R. D., "Presynaptic inhibition in the vertebrate central nervous system," Ergebn. Physicol., Vol. 63 pp. 20-86, 1971).
More recent studies (Eriksson, M. B. E., Sjolund, B. H. and Nielzen, S., "Long term results of peripheral conditioning stimulation as an analgesic measure in chronic pain, " Pain, Vol. 6, pp. 335-347, 1979) have shown that TENS efficacy can be greatly enhanced for some patients by supplementing new stimulation techniques when unsatisfactory results are obtained with conventional stimulation. One popular technique incorporates experience from Chinese electroacupuncture. The discovery that the effects of this technique, as well as those from acupuncture, can be reversed with an opioid antagonist, e.g. naloxone hydrochloride (Sjolund, B. H. and Eriksson, M. B. E., "The influence of naloxone on analgesia produced by peripheral conditioning stimulation", Brain Res., Vol. 173, pp. 295-301, 1979, and Mayer, D. J., Price, D. D., and Rafii, A., "Antagonism of acupuncture analgesia in man by the narcotic atagonic naloxone", Brain Res., Vol. 121, pp. 368-372, 1977) suggested the possibility of an endogenous opiate system responsible for pain control.
Since 1975, several endogenous, morphine-like peptides have been isolated (Hughes, J. et al, "Identification of two related pentapeptides from the brain with potent opiate agonist activity", Nature, Vol. 258, p. 577, 1975), including endorphins which have been found in numerous locations within the central nervous system (Matsukura, S. et al, "The regional distribution of immunoreactive beta-endorphin in the monkey brain", Brain Res., Vol. 159, p. 228, 1978).
The above results have led some researchers (Eriksson, M. B. E., Sjolund, B. H., and Nielzen, S., "Long term results of peripheral conditioning stimulation as an analgesic measure in chronic pain", Pain, Vol. 6, pp. 335-347, 1979) to the conclusion that more than one neurophysiological mechanism is involved in modulating through transcutaneous stimulation. This theory is supported by clinical studies (Mannerheimer, J. S. and Lampe, G. N., "Clinical transcutaneous electrical nerve stimulation", F. A. Davis Company, Philadelphia, pp. 345-348, 1984) that demonstrate the different characteristics shown in Table 1 for conventional and acupuncture-like TENS.
TABLE 1 ______________________________________ Characteristics of TENS Modes Acupuncture- Simultaneous Characteristic Conventional like bimodal ______________________________________ Intensity low high combined Rate high low combined Relief Onset rapid slow rapid Relief Duration short long long Accommodation likely unlikely slight accommodation likely Naloxone no yes reduced Reversible effects Effects ______________________________________
The listed properties for simultaneous bimodal stimulation (i.e. combined stimulation modes) use different stimulation mechanisms and suggest that the effects are additive. The validity of this assumption has been demonstrated in case studies (Mannheimer, J. S. et al. above), but more comprehensive research is needed.
Researchers have found that relevant electrical signal characteristics which must be examined in attempting to treat a painful sensation include the signal waveform, pulse repetition frequency, pulse duration, pulse amplitude and pulse modulation characteristics.